Fix bug in serializing to xml or json where both :only and :except are passed

There was a bug in determining if the uploader should be serializer
when both :only and :except were passed.

This bug was especially important with ActiveRecord's to_xml
implementation, which adds an additional :expect => :type to the
options hash. This made that, althought I only was passing :only, the
bug were discovered.
Revert "Fix bug in serializing to xml or json where both :only and :except are passed"

This reverts commit f74cef93364acfb59cf27fa519119dd0ac53f1dc.